With conventional slip rings for the transmission of signals or for transmitting minor and medium currents, metal wires are preferably employed which run on round sliprings. In such a design, the metal spring is guided by an appropriate holder means relative to the slipring in such a manner that it is constantly maintained in a mechanically biased condition. This bias is required in order to ensure that a proper contact will be continuously maintained even in the case of positional tolerances and movements of the spring relative to the slipring. An example of such a locating device is disclosed in the U.S. Pat. No. 3,574,266. Such arrangements with a single contact spring only produce a comparatively high contact noise in operation, i.e. when the slipring is rotating. This contact noise is created by minute movements of the metal spring on the surface of the slipring.
Systems having more than just one metal spring display substantially better contact characteristics. In these cases, a parallel circuit including several possible current paths can be achieved. For example, when the contact between the first contact spring and the slipring is discontinued for a short period the current may continue flowing via a further contact spring. The probability of the second or of further contact wires losing the contact with the slipring at the same time is extremely low. Such a system with two contact wires is described in the U.S. Pat. No. 3,614,726. This system comprises pairs of contact wires fastened by means of soldered joints on a common locating and contacting wire. Even though such a system has good contacting characteristics it can be produced only with great difficulties because the contacting wires, the contact wires and the electrical terminal must be joined by soldering them individually. In the case of a slip ring assembly with a few contacts only, this work is less relevant than in the case of slip ring assemblies with high numbers of contacts. Apart therefrom, the spacing between the individual sliding contact wires is comparatively wide in such an arrangement so that in the case of many contacts consequently very large dimensions of the entire arrangement are achieved.
This problem is solved by an arrangement disclosed in the European Patent specification EP 0 662 736 B1. There, the contact spring is accommodated in a carrier consisting of an electrically conducting material or as printed circuit board coated with an electrically conductive material. In the case of sliprings having a comparatively small diameter, the contact spring may here be inserted into the carrier in a vertical position. With wider slipring diameters, the contact spring is bent closely towards the carrier at an appropriate angle.
This bending operation, however, must mostly be performed by hand, which requires, in its turn, a high expenditure in terms of labour. Moreover, when usual contact wires are used, which consist only of a single wire, the restitution constant is varied as a result of the deformations of the material at the site of the bend (cold hardening). Even though the manual alignment furnishes uniformly oriented contact wires these wires have different restitution constants and hence different forces pressing against the sliprings.